Backport changes from gutenberg#46896 for 6.3

[madhusudhand]

This PR adds the PHP changes for the following Gutenberg PRs:

WordPress/gutenberg#46896

There are no front-end changes in this PR.

Testing instructions:

• Enable supports for blocks such as post-title

src/wp-includes/blocks/post-title/block.json

{
...
"supports": {
  "shadow": true,
  ...
}

In the theme template add shadow attribute as follows.

<!-- wp:post-title {"shadow":"natural"} /-->

Verify the post title UI to have the applied shadow.

[spacedmonkey]

Please ensure that any change comes with a PHPUnit test.

[ramonjd]

@madhusudhand

Thanks for adding this patch.

You can add the following test to tests/phpunit/tests/style-engine/styleEngine.php

diff --git a/tests/phpunit/tests/style-engine/styleEngine.php b/tests/phpunit/tests/style-engine/styleEngine.php
index 616c332095..6ef8700760 100644
--- a/tests/phpunit/tests/style-engine/styleEngine.php
+++ b/tests/phpunit/tests/style-engine/styleEngine.php
@@ -181,6 +181,19 @@ class Tests_wpStyleEngine extends WP_UnitTestCase {
 				),
 			),
 
+			'inline_valid_shadow_style'                => array(
+				'block_styles'    => array(
+					'shadow' => 'inset 5em 1em gold',
+				),
+				'options'         => null,
+				'expected_output' => array(
+					'css'          => 'box-shadow:inset 5em 1em gold;',
+					'declarations' => array(
+						'box-shadow' => 'inset 5em 1em gold',
+					),
+				),
+			),
+
 			'inline_valid_typography_style'                => array(
 				'block_styles'    => array(
 					'typography' => array(

The new block supports will need a test in tests/phpunit/tests/block-supports/shadow.php

You can probably use one of the existing block supports test files as a guide, e.g., spacing.php

Let us know if you need help.

[ramonjd]

I've continued these changes in this PR over here:

• WordPress 6.3 backport: Add box shadow support to blocks #4696

And have added some test coverage

Thank you @madhusudhand !!!

[tellthemachines]

Closing in favour of #4696.